In general, screw compressors used in refrigeration cycles include: a male rotor (main rotor) and a female rotor (sub rotor) whose rotating shafts are substantially parallel to each other and which are rotated in engagement with each other; a main casing (housing) having a bore for housing the male rotor and the female rotor; a discharge casing (housing wall) that covers the opening of the bore in abutment against the discharge side end face of the main casing in the direction of the rotor shafts; a vertical cylindrical oil separator; and an oil sump for collecting oil separated at the oil separator.
One of the vertical cylindrical oil separators is centrifugal oil separator. In the centrifugal oil separator, oil is caused to adhere to a wall surface by centrifugal force induced by a swirl flow in a separation space. The oil adhering to the wall surface flows down along the wall surface and is collected in an oil sump (sump chamber) provided at the lower part. In general, the centrifugal oil separators are so configured that gas flowing therein is discharged from the upper part of the separation space.
As mentioned above, oil contained in gas discharged from the compression mechanism portion of a compressor is separated and recovered by separating action utilizing centrifugal force. An example of these methods is the cyclone separation disclosed in Patent Literatures 1 and 2. In this conventional example, gas and oil discharged from a compression mechanism portion are guided into a cyclone oil separation space provided at the upper part of an oil tank and separated from each other utilizing centrifugal force.